The authorities in Gaza say the Palestinian territory's only power station has shut down because of a lack of fuel.
The closure is believed to be caused by a shortage in fuel being supplied through smuggling tunnels from Egypt.
Power cuts, already common, are expected to increase. The station provides around 30-40% of Gaza's electricity.
The rest of the electricity used by the territory is supplied by Israel.
The Gaza Power Company said the strip would soon be "swimming in a sea of darkness".
Supplies of fuel smuggled into the territory have diminished due to the recent Egyptian political unrest.
Many families and businesses have private generators to avoid the blackouts. But fuel for those is also hard to come by.
This week long queues can be seen outside petrol stations with people worried about filling up their cars.
A statement from the power station called on Egypt to allow more fuel to pass through the tunnels. It also blamed Israel's continuing blockade of the Palestinian territory.
Israel and Egypt imposed sanctions on Gaza after the Islamist movement Hamas came to power in 2007.
Last year Egypt eased restrictions allowing people to travel more easily, but all legal trade is still forbidden and the tunnel industry continues to thrive.